Various devices, such as valves or ejectors, are used to control fluid flow in liquid and gas form. Such devices are often incorporated into a mechanical assembly in order to control the flow of a fluid within the assembly or flows of fluid into or out of the assembly. To increase or decrease such fluid flow, valves or ejectors can have integrated electrical, pneumatic, or mechanical control components. While these active control mechanisms are commonly used, passive control based on the fluid pressure is less common because of difficulties accurately controlling fluid flow or sizing components to ensure effective operation over a wide range of conditions.
A fuel cell is a device for generating electric power. The chemical energy from a fuel is converted into electricity through a chemical reaction with oxygen or other oxidizing agent. The chemical reaction typically yields electricity, heat, and water. In operation, fuel cells usually require controlled flows of fuel, oxidizing agent, or cooling fluid.
A fuel cell can include an anode in an anode compartment, a cathode in a cathode compartment, and an electrolyte that allows charges to move between the anode and cathode. Electrons are drawn from the anode to the cathode through an electric load circuit, producing electricity. To vary electrical output, valves, ejectors, or other flow devices can be configured to control fluid flows to one or more compartments.
In some examples, a flow of fuel is supplied to an anode compartment, and a flow of oxygen containing gas (e.g., air) is fed to a cathode compartment. The fuel can flow continuously through the anode compartment while a portion of the fuel undergoes an electrochemical reaction in the anode compartment, as represented by the equation below.2H2→4H++4e−
Electrons produced by the anode electrochemical reaction are drawn from the anode to the cathode through an electric load circuit, producing direct-current electricity. The positively charged ions produced by the reaction are drawn from the anode through the electrolyte to the cathode. An electrolyte can be configured to prevent the passage of negatively charged electrons while allowing the passage of positively charged ions.
Following passage of the positively charged ions through the electrolyte, the ions can combine in the cathode compartment with electrons that have passed through the electric load circuit. The combination can form a cathode electrochemical reaction in which water is produced from the reduction of oxygen, as represented by the equation below.O2+4H++4e−→>2H2O
The amount of fuel oxidized in the anode compartment can be dependent on the amount of power required from the electric load circuit. Not all fuel supplied to the anode compartment is oxidized as a portion of the fuel is discharged from the anode compartment.
To increase the overall efficiency of the fuel cell, the outlet from the anode compartment can flow back to the inlet of the anode compartment by way of a recirculation loop. To enable the fuel cell to continuously output power, fuel must be introduced into the recirculation loop to replace the fuel that was oxidized in the anode compartment. The rate at which fuel is introduced into the recirculation loop will depend on the load being applied to the electrical circuit; the greater the load, the more fuel is required.
A flow of fuel introduced into the recirculation loop can be controlled by a variety of devices, including valves or ejectors. Supplying an appropriate amount of fuel to the recirculation loop when a fuel cell ramps up from minimum to maximum power output, and vice versa, may require multiple ejectors of varying sizes or a control valve capable of throttling the flow. Multiple ejectors with different size nozzles, as well as control valves, can be costly and can increase a device's complexity.
Some prior art devices have reduced the need for multiple ejectors by using variable flow ejectors, while others have used a control valve in combination with an ejector. For example, U.S. Pat. No. 6,858,340 discloses a variable flow ejector for use in a fuel cell system. Two diaphragms within the ejector control needle movement relative to the nozzle to regulate fluid flow through the ejector. U.S. Pat. No. 7,536,864 and U.S. Pat. No. 6,779,360 use an actuator to control the nozzle opening. And U.S. Patent Application No. 2010/0068579 discloses a control valve used in conjunction with an ejector.
However, none of these valves and ejectors operate with passive control because they all require some form of active control system. For example, multiple fluids are used to deform multiple diaphragms, a managed actuator maneuvers a ram, a control actuator positions a needle, or a control valve throttles the flow based on downstream feedback. The present disclosure overcomes at least some deficiencies of the prior art.
In consideration of the aforementioned circumstances, the present disclosure provides a recirculation device that can be integrated into a fuel cell system. The recirculation device can passively control anode recirculation flow based on anode compartment exhaust pressure. The device may supply fuel to the fuel cell to permit operate over a range of conditions from a minimum to a maximum power output.